Officials in the upscale Swiss mountain resort of St Moritz quarantined employees and guests of two luxury hotels, closed ski schools and kept schoolchildren home on Monday after a dozen positive tests for a highly infectious coronavirus variant.

About 300 employees and 95 guests at the Grand Hotel des Bains Kempinski St Moritz and Badrutt’s Palace Hotel were quarantined. The eastern canton of Grisons ordered everyone to wear masks in the town of 5,200 that prides itself as a birthplace of modern winter sports.

The two hotels confirmed the quarantine, and the Kempinski confirmed that some of its employees had tested positive for the mutated virus.

Authorities had identified mutations common to highly infections coronavirus variants found in South Africa and Britain, though they could not say whether samples matched either variant because the samples had yet to be genetically sequenced.

Those under quarantine will be tested and those receiving positive tests isolated. Those who test negative may be able to depart but must follow quarantine rules once they arrive home.

The nationalities of those affected were not given, but Grisons said hotel guests probably include foreigners.

Switzerland has left ski lifts open despite the coronavirus, leading to occasional headlines involving some of the world’s swankiest resorts, which have continued to attract jet-set visitors at a time when much leisure travel has been halted.

In December, British tourists in places including Verbier were ordered into quarantine. This month, the famed Lauberhorn World Cup downhill in Wengen was cancelled after an infection spike blamed on a British tourist.

Local St Moritz officials defended the decision to keep skiing open, saying mask-wearing and social distancing makes it safe, and letting people ski makes other places less crowded.

-If there are 100 people on the ski pistes, then there will be 100 fewer in the villages- said Christian Gartmann, an official with a COVID-19 task force in the St Moritz area.